Chart projector for testing visual acuity

Abstract

A chart projector for testing visual acuity capable of detecting a brightness of a visual acuity chart which is projected to an examined eye includes at least one image display device which produces visual acuity chart image; a beam splitter; and a photo sensor which detects a brightness of the chart image reflected from the beam splitter to determine a brightness of visual acuity chart image which passes the beam splitter and projected to the examined eye or which detects a brightness of the chart image which passes the beam splitter to determine a brightness of visual acuity chart image reflected from the beam splitter and projected to the examined eye.

What is claimed is: 
     
       1. A chart projector for testing visual acuity, comprising:
 at least one image display device ( 30   a ,  30   b ) which produces visual acuity chart image ( 40   a ,  40   b ) comprising at least a first chart image ( 40   a ) and a second chart image ( 40   b ); 
 a beam splitter ( 50 ), when the first chart image ( 40   a ) is produced in a looking direction of an examined eye ( 5 ), which transmits a part of the first chart image ( 40   a ) to the examined eye ( 5 ), and reflects the other part of the first chart image ( 40   a ) to block the other part to be projected to the examined eye ( 5 ), and when the second chart image ( 40   b ) is produced outside of the looking direction of the examined eye ( 5 ), which reflects a part of the second chart image ( 40   b ) so as to be projected to the examined eye ( 5 ), and transmits the other part of the second chart image ( 40   b ) to block the other part to be projected to the examined eye ( 5 ); and 
 a photo sensor ( 60 ) which detects a brightness of the first chart image ( 40   a ) reflected from the beam splitter ( 50 ) to determine a brightness of the first chart image ( 40   a ) which passes the beam splitter ( 50 ) and projected to the examined eye ( 5 ) or which detects a brightness of the second chart image ( 40   b ) which passes the beam splitter ( 50 ) to determine a brightness of the second chart image ( 40   b ) reflected from the beam splitter ( 50 ) and projected to the examined eye ( 5 ), 
 wherein, when the photo sensor ( 60 ) detects the brightness of the first chart image ( 40   a ) reflected from the beam splitter ( 50 ), the second chart image ( 40   b ) is turned off, and when the photo sensor ( 60 ) detects the brightness of the second chart image ( 40   b ) which passes the beam splitter ( 50 ), the first chart image ( 40   a ) is turned off. 
 
     
     
       2. The chart projector for testing visual acuity of  claim 1 , wherein the photo sensor ( 60 ) is positioned in a direction perpendicular to a direction that the first chart image ( 40   a ) is transmitted through the beam splitter ( 50 ) and projected to the examined eye ( 5 ) or is positioned in a projection direction of the second chart image ( 40   b ) which passes through the beam splitter ( 50 ). 
     
     
       3. The chart projector for testing visual acuity of  claim 1 , wherein the beam splitter ( 50 ) is a half mirror that reflects some of an incident light and transmits some of the incident light. 
     
     
       4. The chart projector for testing visual acuity of  claim 1 , wherein a brightness of the visual acuity chart image ( 40   a ,  40   b ) produced by the image display devices ( 30   a ,  30   b ) is controlled according to the brightness of the visual acuity chart images ( 40   a ,  40   b ) detected by the photo sensor ( 60 ). 
     
     
       5. A chart projector for testing visual acuity, comprising:
 a first image display device ( 30   a ) which projects a first visual acuity chart image ( 40   a ) polarized in a first direction; 
 a second image display device ( 30   b ) which projects a second visual acuity chart image ( 40   b ) polarized in a second direction; 
 a beam splitter ( 50 ) which partially transmits the first visual acuity chart image ( 40   a ) emitted from the first image display device ( 30   a ) as it is to thereby project the first visual acuity chart image ( 40   a ) polarized in the first direction to an examined eye ( 5 ), and partially reflects the second visual acuity chart image ( 40   b ) polarized in the second direction emitted from the second image display device ( 30   b ) to thereby project a second visual acuity chart image ( 40   b ) polarized in a third direction different from the first direction to the examined eye ( 5 ); and 
 a photo sensor ( 60 ) which detects a brightness of the first chart image ( 40   a ) which is produced by the first image display devices ( 30   a ) and reflected from the beam splitter ( 50 ), and thereby determines the brightness of the first chart image ( 40   a ) which is projected to the examined eye ( 5 ), and which detects a brightness of the second chart image ( 40   b ) which is produced by the second image display devices ( 30   b ) and passes through the beam splitter ( 50 ), and thereby to determine the brightness of the second chart image ( 40   a ) which is projected to the examined eye ( 5 ), 
 wherein, when detecting the brightness of the first chart image ( 40   a ) which is produced by the first image display devices ( 30   a ), the second image display devices ( 30   b ) is turned off, and when detecting the brightness of the second chart image ( 40   b ) which is produced by the second image display devices ( 30   b ), the first image display devices ( 30   a ) is turned off. 
 
     
     
       6. The chart projector for testing visual acuity of  claim 5 , wherein the first image display device ( 30   a ) and the second image display device ( 30   b ) are a liquid crystal display device that projects a polarized image. 
     
     
       7. The chart projector for testing visual acuity of  claim 5 , wherein, according to the brightness of the visual acuity chart images ( 40   a ,  40   b ) detected with the photo sensor ( 60 ), the brightness of the first and the second chart images ( 40   a ,  40   b ) projected to the examined eye ( 5 ) is controlled to be same.